Note: Descriptions are shown in the official language in which they were submitted.
` ~16~S~
Bac~g~ound of the Invention
The present invention relates to the preparation of
polymer containing brines useful in various applications
wherein an increase in viscosity, filtrate control or other
functional property is derived from the polymer composition
contained therein.
Polymer containing brines are useful as well servicing
fluids such as driling fluids, workover fluids, completion
fluids, packer fluids, well treating fluids, subterranean
1~ formation treatiny fluids, spacer fluids and hole abandon-
ment fluids and in other applications wherein thickened
aqueous mediums are required. It is known to use hydrophilic
polymers such as hydroxyethyl cellulose (HEC), for example,
as thickening agents for aqueous mediums such as those used
in well servicing fluids. However, such polymers are not
readily hydrated, solvated or dispersed in aqueous solutions
containing one or more water soluble salts of multivalent
cations such as the heavy oil field brines having a density
greater than about 11.6 pounds per gallon (ppg) preferred for
the preparation of well servicing fluids. Elevated tempera-
tures and/or mixing under high shear for extended periods of
time are required for effective thickening of such brines
with hydrophilic polymeric materials in order to obtain a
homogeneous mixture. In many cases, as, for example, in
workover operations, the equipment available for preparing
the well servicing fluids does not really lend itself to such
conditions. Accordingly, it is usually necessary, if it is
desired to use such thickened brines, to prepare them off the
well site or to circulate the fluid in the hot borehole.
~, ,
l ~8~5~
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Summary oE the Invention
It is, therefore, an object of the present invention to
provide a method fcr the prep~ration of thickened polymer
containing brines, especially heavy brines having a density
yreater than 11.6 ppg under conclitions of lo~ shear mixing
without the application of heat.
Other objects and advantages of the inven-tion ~
become apparent Erom the following description thereof,
together with the appended claims.
~ccording to the invention, a suspension of a hydro-
philic polymer and water is formed by generally uniformly
dispersing the polymer in the water~ An inorganic salt having
a positive heat of solution is then added to the suspension,
in the absence of external heating, the amount of salt added
being sufficient to raise the temperature of the dispersion
to above about 160F as a result of the heat of solution of
the salt. This suspension, depending on the density desired,
can be used directly as a well servicing fluid.
In another embodiment of the invention, there is added
to the liquid suspension of the polymer, a sufficient
quantity of a heavy aqueous brine to provide a quantity of a
well servicing fluid of the desired density.
'
lL ~ 688~0
. .~
Descri~tion of the Preferred Embocliments
The hydrophilic polymers useful in the practice of the
invention are articulate organic polymers which are gener-
ally water soluble or water dispersible and which upon
solution or dispersion in an aqueous medium increase the
viscosity o the system but which do not readily hydrate,
solubilize or disperse upon addition to heavy brines having
a density greater than 11.6 ppg and containing soluble
salts of multivalent cations. Such polymers are selected
from the group consisting of cellulose derivatives, water
dispersible starch derivatives, polysaccharide gums, and
mixtures thereof. Exemplary cellu:Lose derivatives are the
carboxyalkyl cellulose ethers, such as carboxymethyl cellu-
lose and carboxyethyl cellulose; hydroxyalky1 cellulose15 ethers suchas hydroxyethyl cellulose and hydroxypropyl
cellulose; and mixed cellulose ethers such as: carboxy-
alkyl hydroxyalkyl cellulose, i.e. carboxymethyl hydroxy-
ethyl cellulose; alkyl hydroxyalkyl cellulose; i.e. methyl
hydroxyethyl cellulose, methyl hydroxypropyl cellulose;
20 ~ alkyl carboxyalkyl cellulose, i.e. ethyl carboxymethyl
cellulose. (See U.S. Patent No. 4,110,230). Exemplary
starch derivatives are the carboxyalkyl starch ethers such
as carboxymethyl starch and carboxyethyl starch; hydroxy-
alkyl starch ether$, such as hydroxyethyl starch and25 hydroxypropyl starch; and mixed starch ethers such as:
carboxyalkyl hydroxyalkyl starch, i.e. carboxymethyl
hydroxyethyl starch; alkyl hydroxyalkyl starch, i.e. methyl
hydroxyethyl starch; alkyl carboxyalkyl starch, i.e. ethyl-
carboxymethyl starch. Exemplary polysaccharide gums
include: the biopolymers such as Xanthomonas (xanthan)
gum; galactomannan gums, such as guar gum, locust bean
gum, tara gum; glucomannan gums; and derivatives thereof,
particularly the hydroxyalkyl derivatives (See U.S.
Patents Nos. 4,021,355 and 4,105,461). Other polymers
which can be used include pre-gelatinized starch powder
and stabilized partially dextrinized polysaccharide
powder, toxic non-ionic.
1 :~ 6 ~
--5--
Particularly preferred are the HEC polymers which are
generally high yield, water so1uble, non-ionic materials
produced by treating cellulose ~7ith so~ium hydroxide
followed by reaction with ethylene oxide. Each anh~dro-
glucose unit in the cellulose molecule has three reactivehydroxy groups. The average number of moles of the ethylene
oxide that b~comes attached to each anhydroglucose unit in
cellulose is cal]ed moles of substituent combined. In
general, the greater the degree of substitution, the greater
the water solubility. In general, it is preferred to use H~C
polymers having as high a mole substitution as possible.
Usually, upon the addition of one of the dry particulate
hydrophilic polymers described above to aqueous mediums such
as brines, the polymer particles undergo surface hydration
preventing the interior of the particle from readily
hydrating, solvating or otherwise dispersing in the aqueous
medium. Accordingly, high shear, long mixing times and/or
elevated temperatures rnust be applied in order to obtain a
homogeneous system. Using the method of the present
invention, the hydrophilic polymers readily hydrate,
dissolve or disperse in the aqueous brine at relatively low
shear and a~bient temperatures.
In the initial step of the method, the hydrophilic
polymer and water as, for example, fresh water, distilled
water, etc., are admixed under conditions so as to provide a
uniform dispersion of the polymer in the water. The term
"uniform dispersion" as used herein refers to a condition in
which the polymer and water form a generally homogeneous
system whether it be a solution or a mixture in which discrete
polymer particles are generally uniformly distributed
through the suspension of polymer and water. ~he polymer and
water can be admixed by conventional mixing techniques and no
special conditions of temperature, mixing times or other such
parameters are required. It is only sufficient that the
polymer and water be admixed sufficiently to provide the
uniform dispersion of the polymer suspension in the water.
In the next step of the method, an inorganic salt(s) is
8 ~ 0
added, in dry form, to the suspension of the polymer and
water, the sall: beiny of a type which has a positive heat of
solution and brine generates heat upon dissolving in water.
The amount of the inorganic salt added to the polymer
suspension will be such as to provide a temperature of above
about 160F as a result of the heat of solution of the salt
and without the addition of external heating. Dissolving of
the salt in the polymer suspension can be conducted with usual
mixing techniques.
The inorganic salt or salts which can be employed in the
second step of the method are any water soluble salts which
generate heat upon dissolving in water and which preferably
form brines which are useful in hydrocarbon recovery
operations. Preferred salts are those selected from the
group consisting of calcium chloride, calcium bromide, zinc
chloride, zinc bromide, and mixtures thereof. As noted,
preferably the amount of salt added should be such as to raise
the temperature of the polymer/water suspension to above
about 160F. However, it is preferred that the amount of salt
added be such as to raise the temperature to at least 180F
and most preferably to at least 200F. It ~ill be apparent
that different salts have different positive heats of solu-
tion and, therefore, the amount of salt or salts added wil be
dependent upon the particular salt(s~ which are selected.
The polymer/water suspensions prepared as above can
themselves be used as well servicing fluids if the amount of
inorganic salts added are sufficient to achieve the desired
density. Thus, for example, in a typical case, the amount of
polymer, water and inorganic salt admixed may be sufficient
to form a thickened brine of the desired density. More
frequently, however, there is added to the polymer/water
suspension containing the dissolved salt an aqueous brine
solution of a given density, the aqueous brine being added in
an amount so as to provide a well servicing fluid having a
pre-determined density. In this latter embodiment of the
method of the present invention, the polymer, water and
inorganic salt are mixed as above to hydrate the polymer and
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1 1688~0
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form the polymer/water suspension. Following this, the
aqueous brine is admixed with the polymer/water suspension
containing the inorganic salt and the well servicing fluid
thus prepared. The aqueous brines which can be admixed with
the polymer/water suspensions generally contain soluble
salts such as, for example, a soluble salt of an alkali metal,
an alkaline earth metal, a Group Ib metal, a Group IIb meta]
as well as water soluble salts of ammonia and other cations.
Generally speaking, such aq~leous brines contain soluble
salts of multivalent cations, e.g. Zn and Ca. Thus, aqueous
brines comprised of a salt selected from the group consisting
of calcium chloride, calcium bromide, zinc chloride, zinc
bromide, and mixtures thereof are especially preferred. The
aqueous brines will generally have densities ranging from
about 11.6 ppg to about 19.2 ppg.
The amount of the hydrophilic polymer used in the method
of the present invention will be such as to provide a final
concentration of from about 0.1 to about 10 pounds per barrel
(ppb) regardless of whether the ultimate well servicing fluid
comprises (a) the polymer/water suspension prepared by
mixing the polymer, water and the inorganic salt, or (b) the
polymer, water, inorganic salt and an amount of an aqueous
brine.
While the mechanism of the method of the present inven-
tion is not completely understood, it has been found thatbrine solutions prodllced thereby have improved rheological
and filtration properties as opposed to brine solutions
prepared simply by dispersing the hydrophilic polymer, in dry
form, in a brine and then heating the mixture to solvate the
polymer. ~he application of artificial heat to the mixture
of a hydrophilic polymer and a brine while giving some
enhanced results, does not achieve the remarkable results
obtained by the method wherein the polymer is first dispersed
in water and this suspension then brought to elevated
temperature via the mechanism of the natural heat of solution
of the inorganic saltts) dissolving in the polymer/water
suspension. To more fully illustrate the present invention,
1 ~68~50
--8--
the following non-limiting examples are presented.
Unless otherwise indicated~ all physical proper~y
measurements were made in accordance with testing
procedures set forth in STANDARD PROCEDURE FOR TESTING
DRII.LING FLUID, API RP 13B, Seventh Edition, April,
1978. In the following examples, the following
hydrophilic polymers were employed:
Hi Vis CELLE ~ (carboxymethyl cellulose marketed
by N~ Industries, Inc.).
BARAZA ~ (xanthan gum marketed by NL Industries,
Inc.).
NATRASOL~ 250 HHR (hydroxyethyl cellulose marketed
by Hercules Chemical Company).
DRISPA ~ Ipolyanionic cellulose powder marketed by
Drilling Specialities).
BOHRAMYL~ (cross-linked hydroxyethyl starch
marketed by Auebe, N~V.).
IMPERMEX~ (pregelatinized starch powder marketed
by NL Industries, Inc.)-
DEXTRI ~ (stabilized partially dextrinized
polysccharide powder, toxic nonionic marketed by
NL Industries, Inc.).
.
1 ~688~0
g
Example 1
Several hydrophilic polymers were used to prepare
thickened aqueous brines as described below. Approximately
2 g of the polymer was mixed in 204.4 g of water by means of
a Multimixer for about 10 minutes. Thereafter, there was
added to the prehydrated polymer 11~.0 g of CaC12 pellets (94-
97~) and 280.5 g of CaBr2 (91%) followed by 16.8 ml of a 19.2
ppy CaBr2/ZnBr2 brine to bring the density of the resulting
brine to 15.2 ppg. The heat of solution of the added salts
brought each sam~le to boiling (212F). The resulting
thickened mixtures were allowed to stand overnight at ambient
temperature and the rheological and filtration properties of
each mixture were then determined. Rheological properties
were measured using a Fann ~lodel 35A Viscometer and a Brook-
field RVT Viscometer. The filtration properties weremeasured on an API filtration press. The properties reported
are plastic viscosity (PV) cp, Yield Point (YP) lb/100 ft2,
apparent viscosity (AV) cp, 10-second gel strength (GEL 10 s)
lb/lOO ft2, and API filtrate (API-FIL) ml. All filtration
testing was performed after 10 lb/bbl CaCo3 was added as a
bridging agent. Xesults of the measurements made are
presented in Table 1 below. Table 2 gives the same informa-
tion for identical samples after being rolled for 16 hours at
150F.
~ :
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:1 168~50
--10-
Table 1
GEL API
PV YP AV 10 s FIL
CELLEX ~IV - 0 150~ 24.5 1.5
BARAZAN 92 30 109 2.5 6.5
DRISPAC - - 150+41.0 0.5
BOHR~YL 80 4 82 2.0 3.0
I~lPERMEX 72 6 74 2.0 100
DEXTRID 73 6 76 1.5 53
Table 2
GEL API
- PV YP AV 10 s FIL
CELLEX ~V - - 150+ 11.0 0.5
BARAZ~N - - 150~ 6.0 4.5
DRISPAC - - 150+ 9.0 0.5
BOHRAMYL 76 4 78 2.0 1.0
IMPE~5EX 62 4 64 2.0 77
DEXTRID 68 6 71 2.0 89
'~
. ~ . .
.
.
8~50
Example 2
Control thickened aqueous brine solutions were prepared
by adding 2 g of each of the dry polymers eTnployed in Example
1 to a pre-made 15.2 ppg brine prepared by mixing 21~.2 g o
H2O, 119.5 g of CaC12 , 2~4 g -of CaBr2 and 16.2 ml of a
19.2 ppg CaBr2/ZnBr2 brine. Data on the rheological and
filtration properties of the control samples after standing
overnight are presented in Table 3 below while similar data
on identical samples after being rolled for 16 hours at 150F
are presented in Table 4 below. These data compared to those
in Tables 1 and 2 demonstrate that the brines prepared by the
method of the invention (Example 1) wherein the polymer is
first hydrated and the dry salts added thereto exhibit
superior viscosity and give lo~er filtrates in every case
before hot rolling and in substantially all cases after hot
rolling.
,.~
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-12-
Table 3
GEL API
_ YP AV 10 s FIL_
CELLEX HV 54 0 54 2.0 180
BARAZAN 46 0 46 1.5 201.
DRISPAC 55 1 55 1.5 174
BOHRAMYL 49 1 49 1.0 190
IMPEP~IEX 51 1 52 2.0 172
DEXTRID 51 1 51 1.5 170
Table 4
GEL API
PV YP AV 10 s FIL
CELLEX HV 49 0 50 2.0 250
BARAZAN 67 - 67 1.5
DRISPAC 50 3 52 1.5 262
BOHRAMYL 73 - 71 1~5 6
IMPE~IEX 67 6 70 2.0 42
DEXTRID 65 - 64 1.5 6
~ . ` ": '
,
.
~ 1~88~0
-13-
Example 3
Using the method described in Example 1, polymer con-
taining aqueous brines of several different densities wereprepared. Five grarns of Hi Vis Cellex were prehydrated in
water by mixiny for 10 minutes. Dry CaC12 pellets~7ere added
to the prehydrated polymer with mixiny to obtain a }li Vis
Cellex concentrate of 11~6 ppy density. One hundred forty m]
of the concentrate was added to 210 ml of an aqueous brine of
11.6ppg density to achieve a 2 ppb polymer concentration. In
the same manner, heavy aqueous brines of 14.2 and 17.0 were
prepared. The composition of each of the a~ueous brines is
listed in Table 5 below.
Table 5
11.6 14.2 17.0
Water, ml 299.6 234.2 1]2.2
CaC12 g 197.7 137.9 62.6
CaBr2, g ~ 224.3 154.1
19.2 ppg brine, ml - - 166.6
:: `
1 lB~850
Control samples of thickened aqueous brines were
prepared by mixing 2 g of the dry Hi Vis Cellex with premade
brines having densities of 11.6, 14.2 and 17.0 ppg, respec-
tively. Rheological and filtration measurements of the
samples prepared by the method of Example 1 and the control
samples wcre made as described in the foregoing examples.
Results are presented in Table 6. In Table 7, the data
obtained on all the samples after hot rolling at 150F for 16
hours are presented. It is obvious from these data that the
apparent viscosities of the brines prepared by the method of
the invention have values twice as large or more than the
controls. The superior filtration properties of the samples
prepared by the method of the invention are readily evident
as well from a comparison of these data.
~ ~6~5~
--15--
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1 16~0
-16-
Exam~le 4
Brines having a density of 15.4 ppg and containing 1 ppb
carboxymethyl cellulose, either Hi Vis CELLEX (high Vis-
cosity Grade) or DRISPAC, were prepared by adding the polymer
to 176 ml (equivalent to 0.5036 bbl) water and mixing to
dissolve the polymer. Thereafter, there were added, while
mixing, 114 g CaC12 (95%) and 180 g CaBr2 (91~) (equivalent
to 114 and 180 ppb, respectively). The heat of solution of
these salts increased the temperature to 212F. The API
rheology and fluid loss was determined on these viscous
solutions after cooling to room temperature. The data
obtained are given in Table 8.
~ ~6~850
-17 -
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-18-
Example 5
Various density brines containing 1.5 ppb hydroxyethyl
cellulose (NATR~SOL 250 H~IR) were prepared ~y mixing the
polymer with the amount of water indicated in Table 9. As the
polymer hydrated in the water r the viscosity increased.
Thereafter, the indicated amount of CaC12 (95~ active) was
added while mixing. The heat of solution of the CaC]2
increased the temperature about 180F and the solution became
- more viscous. The indicated amount of a 14.2 ppg CaBr2
solution was slowly added followed by the indicated amount oE
a 19.2 ppg ZnBr2/CaBr2 solution. After cooling to room
temperature in one hour, the API rheology and fluid loss were
obtained. The solutions were then rolled at 150F for 16
hours, cooled to room temperature, and the API rheology and
fluid loss determined. The data are given in Table 9.
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-20-
Example 6
Three Hi Vis Cellex polymer concentrates were prepared
by dispersing 2 grams of the polymer in 3.89 ml of water. One
concentrate (Control Sample) was diluted with 155.5 ml of H2O
followed by the addition of 114.0 grams of CaC12, 280.5 gramc
of CaBr2 and 16.8 ml of 19.2 ppg CaBr2/ZnBr2 brine. The
temperature of this sample reached 212F.
A second concentrate (Sample A) was added to a brine
solution at room temperature. I'he brine was prepared with
155.5 ml of H2O, 114.0 grams of CaC12, 280.5 grams of CaBr2,
and 16.8 ml of 19.2 ppg CaBr2/ZnBr2 brine. The mixing in of
the concentrate caused heat evolution, bringing the sample
temperature to 114F. It was noted that insoluble clumps of
carboxymethyl cellulose formed immediately. When cooled
overnight, a large amount of suspended strings were formed
which eventually floated to the surface. It did not appear
that any of the polymer concentrate went into the brine
solution.
A third concentrate (Sample B~ was prepared as in the
case of Sample A and once again heat was evolved when the
concentrate was mixed in, the temperature reaching 111F.
Following this, Sample B was rolled at 212F for 3 hours in
an aging cell. Sample temperature was measured at 160F after
aging. Although some suspended strings of polymer formed and
floated to the top, most of the polymeric concentrate appears
to have been dispersed.
The above three samples were then rolled for 64 hours at
150F. ~ollowing cooling, they were run on a Brookfield
Viscometer at 50 rpm. The Control Sample maintained a reading
of 1590 cp and exhibited a smooth consistency, as before
rolling.
Mosty of the insoluble clumps and all of the suspended
strings dissolved in Sample A. The Brookfield reading was,
nevertheless, only 180 cp.
Sample B, which appeared homogeneous, showed a Brook-
field reading Oc 250 cp.
From the above results, it can be seen that simply pre-
-
1 ~ 6~50
-21-
hydrating the polymer in water alone (Sample A) is not thc
mechanism of the salt activated method of the present inven-
t' tion. In other words, it is also necessary, following
dispersion of the polymer in water, that the dry, positive
heat of solution salt(s) be added to the polymer concen-
trates. While the application of art:ificial heat (rolling at
212F) brings some response (250 cp Brookfield reading on
Sample B, as compared to ]80 cp Brookfield reading on Sample
A), the effect is still no where the 1590 cp Brookfield
reading used on the Control Sample prepared by the salt
activated method.
~ 16~850
-22-
~- The invention may be embodied in other specific forms
without departing from the spirit or essential character-
istics thereof. The present embodiments are therefore to be
considered in all respects as illustrative and not restric-
tive, the scope of the invention being indicated by the
appended claims rather than by the foregoing description, and
all changes which co~e within the meaning and range of
equivalence of the claims are therefore intended to be
embraced therein.
, . . .
.
